Running debugpy with embedded interpreter on Windows

[maxbachmann]

I have an application that embeds Python 3.11. I can successfully attach debugpy from vs code using:

        {
            "name": "Python Debugger: Attach using Process Id",
            "type": "debugpy",
            "request": "attach",
            "processId": "${command:pickProcess}",
        },

However it doesn't stop at any breakpoints. Neither does it if I press the pause button. When enabling debugpy logs I can see that it's sending the corresponding requests for the Pause and breakpoints. E.g. for the Pause Request I get:

20.42s - Process PauseRequest: {
    "arguments": {
        "threadId": "*"
    },
    "command": "pause",
    "seq": 14,
    "type": "request"
}

0.00s - Suspending all threads except: <_MainThread(MainThread, started 13832)>
0.00s - Unable to get topmost frame for thread: <_DummyThread(Dummy-2, started daemon 22796)>, thread.ident: 22796, id(thread): 1967273231712
Current frames: {6616: <frame at 0x000001CA0CED6650, file '<executablePath>\\Lib\\threading.py', line 324, code wait>, 18372: <frame at 0x000001CA0CED6250, file '<executablePath>\\Lib\\threading.py', line 324, code wait>, 21616: <frame at 0x000001CA0CED6350, file '<executablePath>\\Lib\\threading.py', line 324, code wait>, 22968: <frame at 0x000001CA0CED6750, file 'c:\\Users\\max\\.vscode\\extensions\\ms-python.debugpy-2025.0.0-win32-x64\\bundled\\libs\\debugpy\\_vendored\\pydevd\\_pydevd_bundle\\pydevd_additional_thread_info_regular.py', line 187, code get_topmost_frame>, 812: <frame at 0x000001CA0CED6550, file '<executablePath>\\Lib\\threading.py', line 324, code wait>, 3828: <frame at 0x000001CA0AC9EF10, file '<executablePath>\\Lib\\asyncio\\windows_events.py', line 812, code _poll>, 13832: <frame at 0x000001CA786498E0, file '<executablePath>\\<myMainFile>.py', line 306, code main>}.
GEVENT_SUPPORT: False
0.00s - sending cmd (http_json) -->           CMD_RETURN {"type": "response", "request_seq": 14, "success": true, "command": "pause", "seq": 38, "pydevd_cmd_id": 502}

On Linux I can debug the application just fine. However there we use a slightly different setup (we link the system Python instead of a self built CPython version + we use Python 3.11 instead of 3.13).

I am a bit lost as to what could cause this. Any pointers would be helpful.
Let me know if there is additional information that would help debug what's going wrong.

[rchiodo]

That should be normal for a non python application. There are threads running that don't have python code in them.

What did the stack trace request after that point show?

Additionally, if you enable DEBUG_PYDEVD_PATHS_TRANSLATION=True as an environment variable, it should print out more information about why the breakpoints aren't binding. Native apps embedding python might load your code as a string for example, so you wouldn't be able to set breakpoints ahead of time. You'd have to add breakpoint() into your code.

[maxbachmann]

What did the stack trace request after that point show?

That was the end.

Additionally, if you enable DEBUG_PYDEVD_PATHS_TRANSLATION=True as an environment variable, it should print out more information about why the breakpoints aren't binding

When setting a breakpoint in vs code I get

16.26s - Process SetBreakpointsRequest: {
    "arguments": {
        "breakpoints": [
            {
                "line": 384
            }
        ],
        "lines": [
            384
        ],
        "source": {
            "name": "<myFileName>",
            "path": "<myFile>"
        },
        "sourceModified": false
    },
    "command": "setBreakpoints",
    "seq": 29,
    "type": "request"
}

0.00s - Request for breakpoint in: <myFile> line: 384
0.00s - Breakpoint (after path translation) in: <myFile> line: 384
0.03s - Added breakpoint:<myFile> - line:384 - func_name:None

0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - wait
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - wait
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\pydevd.py - _on_run
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_daemon_thread.py - run
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap_inner
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydev_bundle\pydev_monkey.py - __call__
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - wait
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - wait
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\pydevd.py - _on_run
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_daemon_thread.py - run
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap_inner
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydev_bundle\pydev_monkey.py - __call__
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\pydevd.py - set_tracing_for_untraced_contexts
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\pydevd.py - on_breakpoints_changed
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_api.py - add_breakpoint
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_process_net_command_json.py - on_setbreakpoints_request
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_process_net_command_json.py - process_net_command_json
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py - _on_run
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_daemon_thread.py - run
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap_inner
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydev_bundle\pydev_monkey.py - __call__
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - wait
0.00s - SKIP set tracing of frame: <myLibPath>\queue.py - get
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_comm.py - _on_run
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_daemon_thread.py - run
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap_inner
0.00s - SKIP set tracing of frame: <myLibPath>\threading.py - _bootstrap
0.00s - SKIP set tracing of frame: <vsCodePath>\extensions\ms-python.debugpy-2025.0.0-win32-x64\bundled\libs\debugpy\_vendored\pydevd\_pydev_bundle\pydev_monkey.py - __call__
0.00s - sending cmd (http_json) -->           CMD_RETURN {"type": "response", "request_seq": 29, "success": true, "command": "setBreakpoints", "body": {"breakpoints": [{"verified": true, "id": 21, "source": {"name": "<myFileName>", "path": "<myFile>"}, "line": 384}]}, "seq": 118, "pydevd_cmd_id": 502}

Native apps embedding python might load your code as a string for example, so you wouldn't be able to set breakpoints ahead of time.

We use PyMarshal_ReadObjectFromString/Py_CompileString + PyImport_ExecCodeModule for parts of the imports, but not those specific ones.

You'd have to add breakpoint() into your code

This works as expected 👍
After posting I realized that you added back support for the mixed mode debugger in visual studio and it's available in the vs studio preview. This works as expected so thanks a ton for that 😉
I would still be interested into why it's not working via debugpy though.

[rchiodo]

Are you saying breakpoints work in Visual Studio (mixed mode), but they don't in VS Code for the same app? I mean it makes sense, it's two different debuggers. But theoretically they should be searching for breakpoints the same way.

But in debugpy if the breakpoints aren't being hit, that generally means debugpy doesn't think that code is running (or it already ran). The tracing of frame output makes it look like that code isn't running.

If you're running a C++ app and it runs a script, you have to pause the script in order to attach debugpy. That might be what you're hitting. Whereas in Visual Studio with mixed mode, you actually attach a C++ debugger and it just translates python stack frames into python code, so you don't have to pause in the script.

[maxbachmann]

Ah sorry what I had working was

• VS Code / Debugpy Windows works when setting breakpoint() in the code
• VS Code / Debugpy Linux works when setting breakpoints in the editor at runtime as well
• Visual Studio mixed mode works when setting breakpoints in the editor at runtime as well

If you're running a C++ app and it runs a script, you have to pause the script in order to attach debugpy. That might be what you're hitting. Whereas in Visual Studio with mixed mode, you actually attach a C++ debugger and it just translates python stack frames into python code, so you don't have to pause in the script.

Looks like that's it. If I:

• set a breakpoint in the code
• connect via debugpy
• proceed until the breakpoint in the application
• press continue

I can set breakpoints in VS Code and they work as expected.